JP5661582B2 - Precursor for producing Nb3Sn superconducting wire and Nb3Sn superconducting wire - Google Patents

Description

The present invention, _Nb 3 Sn superconducting wire precursor for manufacturing used in the production of _Nb 3 Sn superconducting wire, and to a _Nb 3 Sn superconducting wire produced using the precursor.

Patent Document 1 describes a conventional Nb ₃ Sn superconducting wire. This superconducting wire is used as a winding of a coil of a superconducting magnet. This superconducting magnet is used in nuclear magnetic resonance (NMR) analyzers, physical property evaluation apparatuses, power storage, fusion reactors, and the like. As the superconducting magnet has a higher magnetic field and larger diameter (advanced application), the electromagnetic force (hoop force) acting on the superconducting wire becomes larger, and therefore there is a demand for improving the strength of the superconducting wire at low temperatures.

  Patent Documents 1 to 3 describe superconducting wires that are improved in strength. Patent Document 1 describes a technique in which a superconducting wire is reinforced with alumina-dispersed copper. Patent Documents 2 and 3 describe techniques in which a superconducting wire is reinforced with a high-strength material (described later).

Japanese Patent Publication No. 3-55011 Japanese Patent No. 3153539 JP 2003-86032 A

However, these techniques have the following problems.
Patent Document 1 describes a technique in which a superconducting wire is reinforced with alumina-dispersed copper. Alumina-dispersed copper softens after Nb ₃ Sn generation heat treatment, and the strength decreases. In particular, the electromagnetic force applied to the superconducting wire is increasing with the advanced application of the superconducting magnet. However, the superconducting wire described in Patent Document 1 cannot obtain a strength sufficient to withstand this large electromagnetic force.

  Patent Documents 2 and 3 describe techniques in which a superconducting wire is reinforced with a high-strength material. As this high-strength material, Patent Document 2 describes Ta, and Patent Document 3 describes Ta, W, Mo, V, Zr, and Hf. These metals are expensive and difficult to obtain stably (so-called rare metals). Therefore, superconducting wires reinforced with these metals are expensive.

In the techniques described in Patent Documents 2 and 3, the proportion of the Nb ₃ Sn superconducting phase in the cross section of the superconducting wire is reduced by providing the reinforcing member. Therefore, the superconducting properties (critical magnetic field, critical current density) are reduced.

  2 and 3 of Patent Document 3 describe a technique in which a filament reinforcing material (7) is arranged inside Nb or an Nb alloy (6). Further, the reinforcing material (4) described in FIG. 5 of Patent Document 3 is Ta (see Paragraph 0005 of Patent Document 3).

Therefore, an object of the present invention is to provide a precursor for producing an Nb ₃ Sn superconducting wire for producing an Nb ₃ Sn superconducting wire that can improve superconducting characteristics, can be easily mass-produced, and can have high strength.

The present invention is a _Nb 3 Sn superconducting wire precursor for manufacturing used in the production of _Nb 3 Sn superconducting wire. The precursor includes a superconducting matrix portion in which a plurality of Nb-based filaments made of pure Nb or Nb-based alloy are disposed in a Cu-Sn based alloy, a diffusion barrier layer disposed on the outer periphery of the superconducting matrix portion, A stabilizing copper layer disposed on an outer periphery of the diffusion barrier layer; and a reinforcing member disposed in the superconducting matrix portion. The reinforcing member is made of pure Ti or a Ti-based alloy. The outer periphery of the reinforcing member and the Cu—Sn base alloy are in direct contact.

  In the present invention, superconducting characteristics can be improved, mass production can be easily performed, and strength can be increased.

The nb 3 _Sn superconducting wire precursor for manufacturing a cross-sectional view as viewed from the axial direction. FIG. 9 is a view corresponding to FIG.

A precursor 1 (a precursor for producing a Nb ₃ Sn superconducting wire) according to an embodiment of the present invention will be described with reference to FIG. First, a superconducting wire (Nb ₃ Sn superconducting wire) manufactured using the precursor 1 will be described.

The superconducting wire (Nb ₃ Sn superconducting wire) is manufactured by subjecting the precursor 1 to Nb ₃ Sn generation heat treatment to form an Nb ₃ Sn-based superconducting phase (the manufacturing method will be described later). The structure of this superconducting wire in the cross section perpendicular to the axis (cross section orthogonal to the axial direction, cross section viewed from the axial direction) is substantially the same as the structure of the cross section perpendicular to the axis of the precursor 1 described later. This superconducting wire is used, for example, as a winding of a coil of a superconducting magnet. When this coil is excited, the superconducting wire receives a force (hoop force) that spreads outward in the radial direction of the coil due to electromagnetic force. As a result, the superconducting wire is distorted by receiving a tensile load in the axial direction. In a superconducting wire, the critical current decreases due to strain (the critical current characteristics deteriorate). Therefore, the strength of the superconducting wire is set so that this distortion can be sufficiently suppressed.

Precursor 1 (precursor for producing Nb ₃ Sn superconducting wire) is a wire used for producing an Nb ₃ Sn superconducting wire produced by a bronze method. The precursor 1 is a precursor at a stage before performing the Nb ₃ Sn generation heat treatment. Although details will be described later, the precursor 1 is a precursor at a stage after drawing a secondary multi-core billet that has been extruded by hydrostatic pressure.

  The shape of the cross section perpendicular to the axis of the precursor 1 is formed so that dead space can be reduced when a coil is formed by using a superconducting wire manufactured using the precursor 1 as a winding. Specifically, the precursor 1 has a rectangular cross section perpendicular to the axis (a rectangle including a square). That is, the precursor 1 is a flat wire. The “rectangular shape” includes a rectangular shape having four rounded corners. The closer the four corners of the rectangle are to a right angle, the less dead space. However, it is a necessary condition for the “rectangular shape” that there is a straight line portion between two corners of the rectangle (excluding the diagonal). More specifically, the outer periphery of the cross section perpendicular to the axis of the precursor 1 includes two parallel straight lines and two parallel straight lines orthogonal to the two straight lines. It is a necessary condition (the above “parallel” and “orthogonal” may be “substantially parallel” and “substantially orthogonal”). When the long side length of the cross section perpendicular to the axis of the precursor 1 is W and the short side length is H, the long side length W / short side length H is, for example, 1.2 to 2.0. Yes (may be outside this range). The shape of the cross section perpendicular to the axis of the precursor 1 may be a shape other than a rectangular shape such as a circle or an ellipse.

  The precursor 1 includes a superconducting matrix portion 2, a diffusion barrier layer 6 and a stabilizing copper layer 7 disposed on the radially outer side of the superconducting matrix portion 2, and a reinforcing member disposed on the radially inner side of the superconducting matrix portion 2. 8.

  The superconducting matrix portion 2 has a structure in which a plurality of Nb-based filaments 5 are arranged in a Cu—Sn-based alloy (bronze matrix portion 4). The superconducting matrix portion 2 has a structure in which a plurality of multi-core portions 3 such as tens, hundreds, or thousands are arranged, for example (FIG. 1 illustrates a part of the plurality of multi-core portions 3. ing). Each of the plurality of multi-core portions 3 includes a bronze matrix portion 4 and a plurality of Nb-based filaments 5 arranged in the bronze matrix portion 4.

  The shape of the cross section perpendicular to the axis of the bronze matrix portion 4 (bronze base material) is, for example, a hexagon (may be a circle or the like). The bronze matrix portion 4 is made of a Cu—Sn base alloy. In addition to Ti diffusion (described later) from the reinforcing member 8, the Cu—Sn base alloy may contain, for example, about 0.3 to 0.5 mass% of Ti. As a result of diffusion of Ti from the reinforcing member 8, the Cu—Sn base alloy may contain, for example, about 0.3 to 0.5 mass% of Ti. The Cu—Sn base alloy may contain elements other than Ti.

The higher the Sn concentration in the Cu—Sn base alloy forming the bronze matrix portion 4 (hereinafter also simply referred to as “Sn concentration”), the higher the critical current density (Jc) (produced using the precursor 1). The critical current density of the superconducting wire is increased). The Sn concentration is appropriately set according to the required critical current density. Specifically, for example, the Sn concentration is 13.5% by mass or more, preferably 14% by mass or more, and more preferably 15% by mass or more. Moreover, Sn concentration can be normally raised to 15.6 mass%. Furthermore, if at least one of Ti and Zr is contained in the Cu—Sn based alloy, the Sn concentration can be increased to 19% by mass.
This Sn concentration will be described in more detail. The Sn concentration cannot usually be greater than 15.6% by mass. This is because Cu—Sn intermetallic compounds are produced when Sn is contained in the Cu—Sn base alloy in excess of 15.6% by mass. A typical example of the Cu—Sn intermetallic compound is “δ phase”. Since this δ phase is hard and poor in ductility, the workability at the time of manufacturing the precursor 1 (the workability of the surface-reduction process described later) is deteriorated. Therefore, at least one of Ti and Zr is contained in the Cu—Sn based alloy. Then, the δ phase in the Cu—Sn base alloy can be eliminated. As a result, more Sn than 15.6% by mass, which is considered to be a solid solution limit, can be contained in the Cu—Sn base alloy. Specifically, the Sn concentration can be increased to 19% by mass.

  The Nb-based filament 5 is made of pure Nb or an Nb-based alloy. This pure Nb may contain a trace amount (for example, less than 0.5% by mass) of impurities. This Nb-based alloy is an alloy containing about 10% by mass to 0.5% by mass of an additive element (for example, Ta, Hf, Zr, Ti, etc.). For example, seven Nb-based filaments 5 are arranged in one multi-core portion 3 (6 or less or 8 or more may be used). In FIG. 1, only one Nb-based filament 5 among the plurality of Nb-based filaments 5 is given a reference numeral. The shape of the Nb-based filament 5 in the cross section perpendicular to the axis is, for example, a circle (not necessarily a circle).

  If the diameter of this Nb-based filament 5 (or the equivalent diameter when the cross section perpendicular to the axis is not circular) is reduced, the critical current density increases. However, when the diameter of the Nb-based filament 5 is reduced, the n value decreases. The n value is an amount indicating the sharpness of dislocation from the superconducting state to the normal conducting state. The ratio (D5 / D8) of the (equivalent) diameter D5 of the Nb-based filament 5 to the equivalent diameter D8 of the reinforcing member 8 (described later) is, for example, 0.001 to 0.015, preferably 0.003 to 0. .011 is set.

The diffusion barrier layer 6 is a layer that suppresses the diffusion of Sn in the superconducting matrix portion 2 to the outside (stabilized copper layer 7) during the Nb ₃ Sn generation heat treatment. The diffusion barrier layer 6 is disposed on the outer periphery (radially outer side) of the superconducting matrix portion 2 and on the inner periphery (radially inner side) of the stabilizing copper layer 7. The diffusion barrier layer 6 includes at least one of an Nb layer and a Ta layer. The innermost peripheral layer of diffusion barrier layer 6 (portion in contact with superconducting matrix portion 2) is preferably a Ta layer. The reason is that when the innermost peripheral layer of the diffusion barrier layer 6 is not a Ta layer but an Nb layer, the Nb layer of the diffusion barrier layer 6 and the Sn in the superconducting matrix portion 2 are subjected to Nb ₃ Sn generation heat treatment. This is because an Nb ₃ Sn-based superconducting phase (hereinafter also simply referred to as “superconducting phase”) is formed in the vicinity of the diffusion barrier layer 6 due to the reaction, and the effective filament diameter increases and the AC loss may increase. Note that the diffusion barrier layer 6 and the superconducting matrix portion 2 do not necessarily have to be adjacent to each other, and there may be, for example, a Cu—Sn base alloy layer (not shown) between them.

  The stabilized copper layer 7 is disposed on the outer periphery (radially outer side) of the diffusion barrier layer 6. The stabilized copper layer 7 is a layer for preventing the superconducting phase from being burned out when an overcurrent flows in the superconducting phase when the superconducting wire is changed from the superconducting state to the normal conducting state. In addition, the shape surrounded by the outer peripheral end of the cross section perpendicular to the axis of the stabilized copper layer 7 is the shape of the cross section perpendicular to the axis of the precursor 1.

  The reinforcing member 8 is a member that reinforces the superconducting wire. The shape of the reinforcing member 8 in a cross section perpendicular to the axis is, for example, substantially elliptical (may be circular or rectangular). The reinforcing member 8 is disposed in the superconducting matrix portion 2. That is, the reinforcing member 8 is disposed radially inward from the outer peripheral side end of the superconducting matrix portion 2, and preferably disposed radially inward from the inner peripheral end of the superconducting matrix portion 2. The reinforcing members 8 are concentratedly arranged at the center of the cross section perpendicular to the axis of the superconducting matrix portion 2 (other arrangements will be described later). The “concentrated arrangement” does not mean that the arrangement is divided (for example, distributed) into a plurality of places, but is arranged in a single place. The phrase “disposed in the center” means that the reinforcing member 8 is disposed in a substantially central region of the cross section perpendicular to the axis of the superconducting matrix portion 2. The reinforcing member 8 may not be disposed at the center (centroid) of the cross section perpendicular to the axis of the superconducting matrix portion 2. More specifically, it is a necessary condition that the entire outer periphery of the cross section perpendicular to the axis of the reinforcing member 8 is inside the superconducting matrix portion 2 to be “centered”. Specifically, for example, when there is a portion where the superconducting matrix portion 2 does not exist between the outer periphery of the cross section perpendicular to the axis of the reinforcing member 8 and the diffusion barrier layer 6, it is not included in the “disposed at the center”.

  The reinforcing member 8 is made of pure Ti or a Ti-based alloy. This pure Ti may contain a trace amount (for example, less than 0.5 mass%) of impurities. Further, the Ti-based alloy forming the reinforcing member 8 is an alloy containing about 10% by mass to 0.5% by mass of an additive element. Ti-based alloys are harder than pure Ti. Therefore, when the reinforcing member 8 is made of pure Ti, the workability at the time of manufacturing the precursor 1 (the workability of the area reduction process described later) is better than when the reinforcing member 8 is made of a Ti-based alloy. Further, when the reinforcing member 8 is formed of a Ti-based alloy, the strength of the reinforcing member 8 (of the superconducting wire) is higher than when the reinforcing member 8 is formed of pure Ti. However, when the additive element in the Ti-based alloy exceeds 10% by mass, the above workability deteriorates, so the additive element is preferably 10% by mass or less.

The area ratio A of the reinforcing member 8 (the area ratio A of the reinforcing member 8 occupying the cross section perpendicular to the axis of the entire precursor 1) is expressed by the following equation.
Area ratio A = (cross-sectional area of the reinforcing member 8 / cross-sectional area of the entire precursor 1) × 100 (%)
The area ratio A is, for example, 5 to 30%. The lower limit of the area ratio A may be larger than 5%, for example, 8%, 10%, 15%, etc. The upper limit of the area ratio A may be smaller than 30%, for example, 20% or 25%. The strength of the superconducting wire increases as the area ratio A increases. However, as the area ratio A increases, the proportion of the superconducting matrix portion 2 (superconducting phase) in the cross section perpendicular to the axis of the entire precursor 1 decreases, and the critical current density per whole cross section perpendicular to the axis of the superconducting wire decreases.

  The outer periphery of the reinforcing member 8 is in direct contact with the bronze matrix portion 4 of the superconducting matrix portion 2. The arrangement of the reinforcing member 8 is for allowing the Ti element in the reinforcing member 8 to diffuse into the bronze matrix portion 4. It is preferable that the entire outer periphery of the reinforcing member 8 is in direct contact with the bronze matrix portion 4 (since Ti easily diffuses). Note that only a part of the outer periphery of the reinforcing member 8 may be in direct contact with the bronze matrix portion 4.

(Manufacturing method)
Next, an example of a method of Nb 3 _Sn superconducting wire by the bronze process. The superconducting wire manufacturing method includes a first step of producing a primary stack material (corresponding to the multi-core portion 3) and a secondary multi-core billet (before the precursor 1 is formed) using the primary stack material or the like. ), A third step in which the secondary multi-core billet is processed to form the precursor 1, and a fourth step in which the precursor 1 is subjected to Nb ₃ Sn generation heat treatment to form a superconducting wire. Prepare.

  The first step is a step of producing a primary stack material (corresponding to the multi-core portion 3; hereinafter, the member name at the stage of the precursor 1 may be simply indicated by parentheses). A primary stack material (multi-core part 3) is produced as follows (a)-(g). (A) A Cu—Sn base alloy rod (bronze matrix portion 4) is prepared. (B) Seven holes are formed in the center and the periphery of the cross section perpendicular to the axis of the Cu-Sn base alloy rod. (C) Insert a pure Nb bar (or Nb base alloy bar) (Nb base filament 5) into the hole. (D) Both ends in the axial direction of the Cu-Sn base alloy rod (multi-core portion 3) having undergone the above (b) and (c) are vacuum-sealed by welding. This vacuum sealed product is referred to as a “primary multi-core billet”. (E) The primary multi-core billet is extruded (reduced area) by the hydrostatic extrusion method. (F) The extruded material is drawn (drawn) by drawing or the like. A plurality of annealings are performed during the wire drawing process. This annealing is performed in order to prevent disconnection due to work hardening of the Cu—Sn base alloy. (G) The drawn wire (bar) is finished to a hexagonal cross-sectional shape with a hexagonal die. Thereby, a primary stack material (multi-core part 3) is produced.

  The second step is a step of producing a secondary multi-core billet using a primary stack material or the like. The secondary multi-core billet is produced as follows (h) to (m). (H) A pure Ti bar (or Ti-based alloy bar) (reinforcing member 8) is prepared. (I) A plurality of primary stack materials (multi-core portion 3) are arranged on the outer periphery of a pure Ti rod (reinforcing member 8). (J) In the case of (i) above, the outer periphery of a pure Ti rod (reinforcing member 8) and the primary stack material (multi-core portion 3) are brought into direct contact. (K) A sheet (diffusion barrier layer 6) of pure Nb or the like is wound around the outer periphery of a plurality of primary stack materials (superconducting matrix portion 2). (L) A material obtained by integrating these members (made through the above (h) to (k)) is inserted into a Cu pipe (stabilized copper layer 7). (M) Both ends in the axial direction of the Cu pipe (stabilized copper layer 7) having undergone the above (l) are vacuum-sealed by welding. This vacuum-sealed product is a “secondary multi-core billet”. In addition, the order of each said process can be changed variously. For example, after inserting a sheet (diffusion barrier layer 6) into a Cu pipe (stabilized copper layer 7) and arranging a plurality of primary stack materials (multi-core portion 3) on the inside thereof, a pure Ti rod (reinforcing member) 8) may be arranged.

  The third step is a step of forming the precursor 1 by processing the secondary multi-core billet. This step is performed as in the following (n) and (o). (N) A secondary multi-core billet is extruded (reducing area) by an isostatic extrusion method. (O) The extruded material is drawn (drawn) by drawing or the like. This wire drawing is performed so that the cross section perpendicular to the axis of the wire finally becomes rectangular. Further, similarly to the above (f), annealing is performed a plurality of times during the wire drawing. Thus, the precursor 1 is manufactured (the product at this stage is “precursor 1”).

The fourth step is a step in which the precursor 1 is subjected to Nb ₃ Sn generation heat treatment (diffusion heat treatment) to obtain a superconducting wire. The Nb ₃ Sn generation heat treatment is performed in a vacuum at, for example, 650 to 720 ° C., for example, for 80 to 200 hours. By this Nb ₃ Sn generation heat treatment, an Nb ₃ Sn compound layer is generated at the interface between the bronze matrix portion 4 (Cu—Sn base alloy) and the Nb base filament 5. Further, the Ti element of the reinforcing member 8 is diffused into the bronze matrix portion 4 by the Nb ₃ Sn generation heat treatment (this diffusion may occur during other heating-related processes). Thus, _Nb 3 Sn superconducting wire is manufactured.

(Experiment)
The “superconducting wire of the example” was manufactured by the above manufacturing method. For comparison, a “comparative superconducting wire” was manufactured. And about each superconducting wire, 0.2% yield strength and critical current were measured.

The superconducting wire of the example was manufactured as follows. The Cu—Sn base alloy rod (bronze matrix portion 4) prepared in the step (a) of the above production method has Cu-15 wt% Sn, a diameter of 150 mm, and an axial length of 500 mm. The pure Nb rod (Nb-based filament 5) inserted into the hole in the step (c) has a diameter of 17 mm and an axial length of 500 mm. The diameter (the diameter of the circumscribed circle of the hexagonal cross section) of the primary stack material (multi-core part 3) produced in the steps (a) to (g) is 3 mm. The pure Ti rod (reinforcing member 8) prepared in the step (h) has a diameter of 60 mm. There are 3000 primary stack members (multi-core portions 3) arranged on the outer periphery of the pure Ti rod (reinforcing member) in the step (i). The Cu pipe (stabilized copper layer 7) used in the step (l) has an outer diameter of 150 mm, an inner diameter of 120 mm, and an axial length of 500 mm. The material of the sheet (diffusion barrier layer 6) wound around the outer periphery of the primary stack material (superconducting matrix portion 2) in the step (k) is pure Nb. The long side length W of the cross section perpendicular to the axis of the precursor 1 manufactured by the steps (a) to (o) is 1 mm. The area ratio A of the reinforcing member 8 occupying the entire cross section perpendicular to the axis of the precursor 1 is 10%. This precursor 1 was subjected to Nb ₃ Sn generation heat treatment (diffusion heat treatment) to obtain the superconducting wire of the example.

  The superconducting wire of the comparative example has the same size and structure as the superconducting wire of the example. However, the material of the reinforcing member 8 is pure Ti in the embodiment, but pure Ta in the comparative example.

  The 0.2% proof stress was measured by immersing the superconducting wire in liquid helium (temperature 4.2 K) and conducting a tensile test of the superconducting wire. The critical current was measured by the four probe method in liquid helium (temperature 4.2 K) under an external magnetic field of 15 T (Tesla).

The experimental results were as follows. The result (ratio) of the superconducting wire of the example when the result of the superconducting wire of the comparative example is 100% is shown.
・ Wire strength (0.2% proof stress @ 4.2K)
Comparative example: 100%, Example: 105%
・ Superconducting properties (critical current @ 15T)
Comparative example: 100%, Example: 120%

  (Wire strength) The 0.2% yield strength of the example was higher than that of the comparative example. This is because the mechanical strength at low temperature is higher for Ti than for Ta. In the examples, the 0.2% proof stress was greater than 250 MPa.

  (Superconducting characteristics) The critical current was higher in the example than in the comparative example. This is because the Ti element of the reinforcing member 8 diffuses into the bronze matrix portion 4 and a Ti addition effect (described later) occurs.

(effect)
Next, the effect of the precursor 1 shown in FIG. 1 will be described. The precursor 1 is used for manufacturing an Nb ₃ Sn superconducting wire. The precursor 1 includes a superconducting matrix portion 2 in which a plurality of Nb-based filaments 5 made of pure Nb or an Nb-based alloy are disposed in a bronze matrix portion 4 (Cu—Sn based alloy), and an outer periphery of the superconducting matrix portion 2. Disposed diffusion barrier layer 6, stabilized copper layer 7 disposed on the outer periphery of diffusion barrier layer 6, and reinforcing member 8 disposed in superconducting matrix portion 2.

(Effect 1-1)
The reinforcing member 8 is made of pure Ti or a Ti-based alloy. Further, the outer periphery of the reinforcing member 8 and the bronze matrix portion 4 are in direct contact. Therefore, Ti element of the reinforcing member 8 is diffused in the bronze matrix portion 4 (in the superconducting matrix portion 2) during Nb ₃ Sn generation heat treatment or the like. Therefore, the superconducting properties (upper critical magnetic field and critical current density in a high magnetic field) of the superconducting wire manufactured by the precursor 1 can be improved.

  This effect will be further described. When the reinforcing member 8 is provided in the precursor 1, the strength of the superconducting wire increases. On the other hand, the area ratio of the superconducting matrix portion 2 occupying the cross section perpendicular to the axis of the precursor 1 (the area ratio of the superconducting phase) decreases. That is, the contact area between the Cu—Sn base alloy (bronze matrix portion 4) and the Nb base filament 5 is reduced. Therefore, simply providing the reinforcing member 8 reduces the superconducting characteristics. However, in the present invention, the superconducting characteristics of the superconducting wire can be improved by the above Ti addition effect. That is, in the present invention, it is possible to suppress a decrease in superconducting characteristics due to the provision of the reinforcing member 8.

(Effect 1-2)
The reinforcing member 8 is made of pure Ti or a Ti-based alloy.
Pure Ti or Ti-based alloy is easy to obtain and cheaper than high strength materials (Ta, W, Mo, V, Zr, Hf, etc.) conventionally used as the reinforcing member 8. Therefore, the precursor 1 can be easily mass-produced.
Pure Ti or a Ti-based alloy has higher mechanical strength characteristics (such as low-temperature brittleness) at a low temperature than alumina-dispersed copper or the like conventionally used as the reinforcing member 8. Therefore, the strength of the superconducting wire manufactured from the precursor 1 can be made higher than before.

(Effect 2)
The reinforcing members 8 are concentrated in the center of the cross section perpendicular to the axis of the superconducting matrix portion 2. Therefore, the reinforcing members 8 can be easily arranged as compared with the case where the reinforcing members 8 are dispersedly arranged in the superconducting matrix portion 2. As a result, the precursor 1 can be easily manufactured.

(Effect 3)
The precursor 1 has a rectangular cross section perpendicular to the axis. Therefore, when the superconducting wire manufactured using the precursor 1 is used as a coil winding, the dead space between the superconducting wires can be reduced as compared with a superconducting wire having a circular cross section perpendicular to the axis. As a result, the current density of this coil can be increased, and a superconducting magnet using this coil can be made compact.

(Effect 4)
The superconducting wire (Nb ₃ Sn superconducting wire) of the present invention is produced by subjecting the precursor 1 to Nb ₃ Sn generation heat treatment to form an Nb ₃ Sn-based superconducting phase. This superconducting wire has the effects (Effect 1) to (Effect 3).

(Other effects 1)
The Sn concentration (Sn concentration) in the Cu—Sn base alloy forming the bronze matrix portion 4 is 13.5% by mass or more. Therefore, the critical current density can be made higher than when the Sn concentration is less than 13.5% by mass. Therefore, it is possible to further suppress the deterioration of the superconducting characteristics due to the provision of the reinforcing member 8.

(Other effects 2)
The reinforcing member 8 is made of pure Ti or a Ti-based alloy. Pure Ti or Ti-based alloy has a higher specific strength (tensile strength / density) than materials conventionally used as the reinforcing member 8 (alumina-dispersed copper, the above-described high-strength material, etc.). Therefore, the superconducting wire manufactured from the precursor 1 can be made lighter than before. As a result, the weight of the superconducting magnet manufactured using this superconducting wire can be reduced, and the support structure of this superconducting magnet can be simplified.

(Modification 1)
FIG. 2 shows a precursor 11 of Modification 1. As shown in FIG. 1, the reinforcing members 8 of the precursor 1 of the above embodiment are concentratedly arranged at the center of the cross section perpendicular to the axis of the superconducting matrix portion 2. On the other hand, as shown in FIG. 2, the reinforcing members 18 may be dispersedly arranged in the superconducting matrix portion 2. Hereinafter, this difference will be further described.

  The precursor 11 includes reinforcing members 18 distributed in the superconducting matrix portion 2 instead of the reinforcing members 8 of the precursor 1 shown in FIG. For example, the reinforcing members 18 are dispersedly arranged by replacing a part of the plurality of multi-core portions 3 of the precursor 1 shown in FIG. 1 with the reinforcing members 18 shown in FIG. In FIG. 2, only some of the plurality of reinforcing members 18 (shown in black) are denoted by reference numerals.

(Modification 2)
Moreover, you may combine the reinforcing member 8 of the precursor 1 shown in FIG. 1, and the reinforcing member 18 of the precursor 11 shown in FIG. That is, the precursor 1 (11) includes a reinforcing member 8 (see FIG. 1) concentrated in the center of the cross section perpendicular to the axis of the superconducting matrix portion 2 and a reinforcing member 18 (see FIG. 1) distributed in the superconducting matrix portion 2. 2)).

1,11 Precursor (Precursor for producing Nb ₃ Sn superconducting wire)
2 Superconducting matrix part 4 Bronze matrix part 4 (Cu-Sn based alloy)
5 Nb-based filament 6 Diffusion barrier layer 7 Stabilized copper layer 8, 18 Reinforcing member

Claims (3)

A precursor used in the manufacture of Nb ₃ Sn superconducting wire,
A superconducting matrix portion in which a plurality of Nb-based filaments made of pure Nb or Nb-based alloy are arranged in a Cu-Sn based alloy;
A diffusion barrier layer disposed on the outer periphery of the superconducting matrix portion;
A stabilized copper layer disposed on an outer periphery of the diffusion barrier layer;
A reinforcing member disposed in the superconducting matrix portion;
With
The reinforcing member is made of pure Ti or a Ti-based alloy,
The outer periphery of the reinforcing member and said Cu-Sn-based alloy directly contacts,
The reinforcing member is concentrated in the center of the cross section perpendicular to the axis of the superconducting matrix portion.
Precursor for producing Nb ₃ Sn superconducting wire. The precursor for producing a Nb ₃ Sn superconducting wire according to claim 1, wherein the cross section perpendicular to the axis is rectangular. Against Nb ₃ Sn superconducting wire precursor for manufacturing according to claim 1 or 2, is subjected to Nb ₃ Sn generated heat treatment is produced by forming a Nb ₃ Sn based superconducting phase, Nb ₃ Sn superconducting wire.

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